1. Field of the Invention
This invention relates to a method for producing a printed wiring board having electronic components, such as LSI (large-scale integrated circuit), enclosed therein.
2. Description of Related Art
Heretofore, a printed wiring board unit, arranged in a casing forming an electronic equipment, has a pre-set wiring pattern formed on its one or both sides, and electronic components, such as LSIs, mounted on a land to form a number of variable electrical circuits. In a certain printed wiring board, used in a miniaturized multi-functional electronic equipment, plural substrates, each carrying a wiring pattern, are layered together, and electronic components are mounted on both sides of the layered structure.
Meanwhile, in a certain printed wiring board, plural substrates are layered together, and electronic components are embedded in the interior, in order to mount a larger number of electronic components on the substrate. The printed wiring board, having electrical components embedded therein, are formed as shown for example in FIGS. 1 to 4. That is, a first wiring pattern 52 is formed on one surface of a first substrate 51, as shown in FIG. 1. On the other surface of the first substrate 51 is formed an electrically conductive layer 53, formed by a copper foil, in order to form a fourth wiring pattern. A via-hole 60 is formed in the first substrate 51 for establishing electrical connection between the first wiring pattern 52 and the fourth wiring pattern as later explained. The via-hole 60 is plated with copper as at 60a. On one surface of the first substrate 51, carrying the first wiring pattern 52, there is provided a spacer 54 for achieving insulation from a second substrate 55 layered on the first substrate 51. On at least one surface of the second substrate 55 is formed a second wiring pattern 56.
The first substrate 51, on which is formed the first wiring pattern 52, and the second substrate 55, on which is formed the second wiring pattern 56, are formed separately from each other. The second substrate 55 is stacked on the spacer 54 and bonded thereto by hot pressing. A via-hole 65 then is formed for electrically connecting the electrically conductive layer 53 of the first substrate 51 and the second wiring pattern 56 of the second substrate 55 and the inside of the via-hole is plated wan copper at 66.
For exposing an area on the first substrate 51 on which to mount an electronic component 57 to outside, an opening 58 is formed by a router 59 in the second substrate 55 and in the spacer 54. Specifically, the router 59 is run along an approximately rectangular path to cut the outer rim of the opening 58, and subsequently the router is run along a staggered path in the interior of the rectangle to form the opening 58 extending through the thicknesses of the substrate 55 and the spacer 54. So, a component mounting portion 61 of the electronic component 57, placed on one surface of the first substrate 51, is exposed to outside via the opening 58 formed in both the substrate 55 and in the spacer 54. On this component mounting portion 61, exposed to outside via the opening 58, the electronic component 57, such as LSI, is mounted and soldered in position. The opening, in which the electronic component 57 has been mounted as described above, a synthetic resin mass 67 is charged by potting.
On the second substrate 55, a third substrate 62 is formed by RCC (resin coated copper foil) molding, as shown in FIG.4. Specifically, the third substrate 62 is formed on the second substrate 55 by press fitting a resin-coated copper foil under vacuum heating. An electrically conductive layer of a copper foil, formed on the third substrate 62, is etched to form a third wiring pattern 63. An electrically conductive layer, provided on the opposite surface of the first substrate 51, is also etched to form a fourth wiring pattern 64. A via-hole 68 then is formed in the third substrate 62 in order to provide for electrical connection between the third wiring pattern 63 provided on the third substrate 62 and the second wiring pattern 56 provided on the second substrate 55. The printed wiring board, prepared as described above, then is checked electrically whether or not the wiring pattern is short-circuited. This electrical check is conducted because the fourth wiring pattern 64 is not formed in the previous step, with the electrical circuit of the printed wiring board being in a short-circuited state.
In the method for producing the printed wiring board, as described above, the opening 58 is formed by the router 59 for mounting the electrical component 57 on the component mounting portion 61 of the first substrate after layering the spacer 54 and the second substrate 55 on the first substrate 51. However, a drill of the router 59 has a tolerance in the vertical direction on the order of xc2x130 xcexcm, so that, if the drill intruding depth is too shallow, the first wiring pattern 52 is not exposed, whereas, if the drill intruding depth is too deep, the first wiring pattern 52 also is cut. So, a thin copper foil cannot be used as the first wiring pattern 52 so that a thin pattern is difficult to form. In addition, the component mounting portion 61 cannot be worked to high planarity.
In the above-described process, the electrical component 57 is mounted on the component mounting portion 61 of the first substrate 51, the third substrate 62 is mounted on the second substrate 55 and finally the printed wiring board is checked electrically. So, if this electrical check has revealed that the printed wiring board is short-circuiting, not only the first to third substrates 51, 55, 62, but also the electrical component 57 are wasted.
It is therefore an object of the present invention to provide a manufacturing method for a printed wiring board whereby a printed wiring board having electronic components enclosed therein can be manufactured easily and efficiently.
According to the present invention, there is provided a method for producing a printed wiring board including the steps of forming a wiring pattern on one surface of a first substrate and forming a component mounting portion for mounting an electronic component thereon, forming an insulating spacer having a first opening formed in registration with the component mounting portion of the first substrate, forming a second substrate, stacking the spacer on the one surface of the first substrate, with the first opening in registration with the component mounting portion, stacking the second substrate on the spacer, pressing together the first substrate, spacer and the second substrate, thus stacked, for bonding the first and second substrates together, boring a second opening in the second substrate, after bonding the first substrate, spacer and the second substrate together, in registration with the first opening, so that the second opening is in continuation to the first opening, for exposing the component mounting portion of the first substrate to outside, mounting an electronic component on the component mounting portion of the first substrate which makes up the bottom of a spacing delimited by the first and second openings, continuing to each other, and filling resin in the spacing, having the electronic component mounted therein, and providing a third substrate on the second substrate to stop the spacing after charing resin in the spacing.
Since the spacing is provided by the spacer provided with the first opening, the second opening may be formed by a router in the second substrate without damaging the component mounting portion of the first substrate.
By forming the spacer by the core material, the first prepreg provided between the core material and the first substrate and the second prepreg provided between the core material 26 and the second substrate, the resin component, such as epoxy resin, is prevented from seeping out around the first and second substrates.
In the step of forming the second substrate, the through-hole is bored in the second substrate at a position overlying the first opening, so that, when the first and second substrates are unified together via the spacer, the spacing delimited by the first and second substrates and the first opening of the spacer may be prevented from becoming a hermetically sealed spacing, that is a spacing maintained in vacuum, thereby preventing the first or second substrate from becoming deformed.
After the first substrate, spacer and the second substrate are bonded together, a further wiring pattern is formed on the other surface of the first substrate 11. At this stage, the substrate is checked electrically. Since the substrate can be checked electrically before mounting the electronic component, wastage of the electronic components may be eliminated even if the substrate is found to be short-circuited.
When pressing the first and second substrates, these first and second substrates, stacked together, are heated under pressure at a temperature lower than the temperature allowed for these component units, to prevent thermal deformation of the component units.
It is noted that, in providing the third substrate on the second substrate, the first substrate, spacer and the second substrate, bonded together, are grounded to prevent the electronic components from being damaged by static charges.
With the manufacturing method for the printed wiring board according to the present invention, in which the spacing is provided by the spacer having the first opening, the second opening may be formed by the router in the second substrate without damaging the component mounting portion of the first substrate. Since it is sufficient to run the router to follow the outer rim of the first opening, the processing time can be shorter than in the conventional method.